Thou Shalt Kill

A grim but true tale of Mormons and murder

In 1984 an unemployed 42-year-old construction worker named Ron Lafferty received a message from God instructing him to kill his brother's wife Brenda and her 15-month-old baby Erica. Four months later, Ron--with the help of another brother, Dan--carried out his divine assignment with a 10-in. boning knife. Jon Krakauer tells the story of the Lafferty brothers in Under the Banner of Heaven (Doubleday; 372 pages).

True crime isn't really Krakauer's beat--he's the author of Into Thin Air, the bestselling account of a disastrous Everest expedition--but he takes an able, earnest stab at it. It turns out that Ron and Dan weren't...